Many synthetic cloth-like materials are available on the market. The synthetic materials are made of thermoplastic and formed as woven and non-woven types. Some of these synthetic cloths include materials generally known as "Tyvek," which is a trademark of E. I. DuPont de Nemours & Co., Wilmington, Del. 19898; "Duraguard" and "Safeguard," which are trademarks of Kimberly-Clark Corporation, Roswell, Ga. 30076; "Celestra," which is a trademark of Crown Zellerbach Corporation, Washougal, Wash. 98671; and "Duralace," which is a trademark of Chicopee Manufacturing Co., Chicopee, Ga. 30501. These materials are utilized as substitutes for cloth and pulp-paper in items such as envelopes and disposable clothes for medical, industrial and retail markets. Many such applications require that the material be joined at a seam, and in this respect some difficulty is encountered in the prior art.
In the prior art, the seams in the material for forming, for example, disposable coveralls, are often formed by sewing it much like cloth, or by using adhesive, including heat-sensitive adhesives. Sewing of the material causes pinholes which makes the completed item of clothing undesirable for use in dust-free and sterilized environments. Use of adhesives to form bonding requires special adhesives and complicates the manufacturing procedure. Furthermore, it is difficult to obtain a good seal bond along a seam by using adhesives.
Various heat seal methods have been attempted, but they have not proved to be satisfactory. In many instances the seal obtained exhibits a "zipper" effect, in that the seal has random intermittent breaks or weak points which affect the quality of the seal at the seam.